Pretty, though I keep pronouncing it "mel-ih-SAHN-dee/mel-ih-SAHN-day" because it looks vaguely Greek to me (yes, I know it's really French. My brain just refuses to believe it), even though I'm pretty sure that pronunciation is all wrong. Still, I definitely like the look of it!
Nicknames could be
Mel,
Lisa,
Lissa, Lissy,
Issy,
Sandy,
Ann, or
Andi /
Andy.